A V(IV) Hydroxyhydrogenomonophosphate with an Intersecting Tunnel Structure: HK4[V10O10(H2O)2(OH)4(PO4)7]·9H2O

A V(IV) hydroxyhydrogenomonophosphate HK4[V10O10(H2O)2(OH)4(PO4)7]·9H2O has been obtained, using hydrothermal conditions. Its structure, closely related to that of (CH3)2NH2K4[V10O10(H2O)2(OH)4(PO4)7]·4H2O, differs from the latter by its I41/a space group (instead of P43). This difference corresponds to a "disordering" of the vanadium atoms, with respect to the dimethyl ammonium phase. It is shown that this disorder, which appears in the form of "V5O22" units distributed at random, does not affect the oxygen framework. The analysis of this complex structure shows that it can be described from the stacking along c of [V8P7O38(OH)4(H2O)2]infinity layers interconnected through layers of isolated VO6 octahedra. In this structure, built up of VO6, VO5OH, and VO4(OH)(H2O) octahedra, of VO4OH pyramids, and of PO4 tetrahedra, large "toffee" tunnels and smaller ones with a tulip-shape section are running along a (or b). The first ones are stuffed with H2O molecules forming aquo tubes, where protons are likely "delocalized," whereas the second ones are occupied by K+ cations.